Sensor system for detecting dimensional variables to be measured on a rotating object

ABSTRACT

A sensor system for detecting at least one dimensional variable of a rotating object ( 30 ) includes a plurality of sensors ( 33 ) disposed on the rotating object ( 30 ) that are sensitive to the dimensional variable and an antenna array ( 11 ) for supplying the sensors ( 33 ) with high-frequency energy and for receiving a high-frequency signal, modulated by the variable to be detected, from the sensors ( 33 ). The sensors are disposed on the object ( 30 ), distributed in the circumferential direction, and the antenna array ( 11 ) has a directional characteristic ( 34 ) for transmission and/or reception which is stationary with respect to a coordinate system not rotating with the object ( 30 ) and which includes only a subregion ( 32 ) of the object ( 30 ).

The present invention relates to a sensor system for remote detection ofat least one dimensional variable, which is measured at a rotatingobject.

BACKGROUND OF THE INVENTION

The capability of remote polling of a sensor is necessary in many kindsof application, especially wherever it is problematic to establish apermanent physical connection between a sensor and an associatedevaluation unit, by way of which connection output signals of the sensorcan be transmitted to the evaluation unit. Such connection problemsarises wherever the sensor is moved relative to the associatedevaluation unit, especially when rotary motions are involved. Examplesof this that can be given are detecting the pressure in a pneumatic tiremounted rotatably on a vehicle, or measuring the torque on a rotatingshaft.

These applications require the transmission of output signals of thesensor electromagnetically, in the broadest sense; that is, thetransmission of radio signals, microwave signals, or light signals. Onepossibility of doing so is to equip the sensor element with its ownpower supply, to furnish the energy needed for the measurement and fortransmitting the output signals. However, this principle quickly reachesits limits because of the attendant costs (battery), the relatively highweight of the sensor unit, and the requisite maintenance, since thebattery has to be replaced after a certain time in operation.

It is therefore desirable to make the sensor entirely passive, or inother words to embody it without its own power supply, in order tocircumvent the problems associated with the battery and to make thesensor smaller, lighter in weight, and less vulnerable.

One example of a sensor system with sensors that can be remotely polledelectromagnetically is discussed in German Patent DE 19 702 768 C1. Thesensor system known from this reference includes the following:

-   -   a sensor, disposed on the rotating object and sensitive to the        dimensional variable, and means for forwarding the signals of        the sensor to a processing device, which means include an        antenna array for supplying the at least one sensor with        high-frequency energy and for receiving a high-frequency signal,        modulated as a function of the variable to be detected, from the        sensor.

This sensor system is suitable for detecting dimensional variables ofthe rotating object that are essentially constant throughout the entireobject, so that the precise location where a measurement is made is notcritical.

However, if it is critical to detect dimensional variables whose valuesare not uniform throughout the object, then the known sensor systemrapidly reaches its limits. Measurements can still be performed insubregions of the rotating object if these subregions rotate jointlywith the object, or in other words if the sensor can be disposed at thesubregion of interest and can rotate jointly with it; but if it iscritical to detect dimensional variables in a subregion of the rotatingobject that is stationary relative to a coordinate system that does notrotate with the object, then the known system is taxed beyond itscapabilities.

SUMMARY OF THE INVENTION

By means of the present invention, a sensor system for detecting atleast one dimensional variable of a rotating object is created thatmakes it possible in a simple way to detect a dimensional variable in asubregion of the rotating object that is stationary with respect to acoordinate system that does not rotate with the object.

These advantages are attained by providing that a plurality of sensorsare disposed on the object, distributed in the circumferentialdirection, and that the antenna array has a directional characteristicfor transmission and/or reception which is stationary with respect to acoordinate system not rotating with the object and which includes onlythe subregion of the object.

In the course of the rotation of the object, many of the sensorsdisposed on it move successively through the subregion, where they cancome to interact with the antenna array. This means that only when theaffected sensors are located in the subregion are they supplied withhigh-frequency energy that enables them to broadcast an answering radiosignal, and/or that an answering radio signal broadcast by the sensorswill be received by the antenna array only when the affected sensor islocated in the subregion.

The subregion can advantageously be a contact face of the object, with asubstrate. It is then possible for instance to measure contact forcesthat are operative between the object and the substrate while the objectis rolling over the substrate.

To keep the system simple and compact, it is preferred that the antennaarray includes a common antenna for both sending high-frequency energyto the sensors and receiving an answering signal from the sensors.

Sensors that are used to detect the same physical variable canexpediently have a spacing in the circumferential direction of theobject that is essentially equivalent to the length of the subregion inthe circumferential direction. In this way, it is assured that over thecourse of the rotation of the object, there is one sensor for theapplicable dimensional variable located in the subregion at all times,so that a continuous measurement of the dimensional variable is assured.

It is especially preferable that the sensors have coding, which makes itpossible to supply high-frequency energy selectively to at least onesensor from among a plurality of sensors located in the subregion, or toreceive selectively from at least one sensor located in the subregion.Such a provision makes it possible to stagger the sensors on thecircumference of the rotating body closer together than would beequivalent to the length of the subregion in the circumferentialdirection; since the sensors can be polled selectively, however, thedimensional variable can be determined with a local resolution that isfiner than the length of the subregion.

Especially easy identification of the sensors is provided for it thesensors form n groups, which are each distributed cyclically over thecircumference of the object.

To assure an unambiguous association of the measured values with thevarious sensors furnishing them, it is preferred that the subregion isdefined such that the sensors of all n groups are never all located init at the same time.

It is also expedient that each sensor has a first resonator, which canbe excited by a modulated measurement frequency of a carrier frequencyof the high-frequency energy, and whose resonant frequency is variableas a function of the dimensional variable. This resonant frequency maybe modulated to an answering radio signal, which the sensor sends to theantenna array, so that from the modulation frequency, a processingdevice connected to the ant can conclude what the value of thedimensional variable to be detected is.

This resonator preferably includes a surface wave resonator or a quartzoscillator as an element capable of oscillation. Also, a discretecomponent that is sensitive to the dimensional variable is preferablyalso incorporated into the first resonator, which makes it possible touse economical standard components as the element capable ofoscillation.

The use of resonators with a resonant frequency that is variable as afunction of the dimensional variable also has the advantage that theaforementioned coding can be achieved by assigning each sensor in thesensor system its own specific resonator tuning range. This makes itpossible, on the basis of the modulation frequency of the answeringradio signal, arriving at the antenna array from a sensor, to concludewhat the identity of the transmitting sensor is.

If the tuning ranges of the individual first resonators of varioussensors partly overlap, then an association of the received answeringradio signal with a sensor can be made taking into account the receptionfield intensity at the antenna array as well. A simpler association isobtained, however, if the resonator tuning ranges of the individualcodings are disjoint.

A preferred application of the sensor system of the invention is thedetection of vectorial variables, in particular forces or accelerations.If for instance the rotating object is a vehicle tire, then detectingsuch variables makes it possible to detect dangerous situations, such asaquaplaning, inadequate adhesion of individual wheels of the vehicle incornering, and so forth, and to generate a warning to the vehicle driveraccordingly.

In such a case, it is often not necessary that all three components ofthe vectorial variable be detected; in the instances given above, it issufficient if the sensors are each designed for detecting two componentsof the dimensional variable that are perpendicular to one another andtangential to the surface of the object. A conclusion as to the value ofa component of the vectorial variable that is oriented radially to thetire can be drawn by measuring the tire pressure, for instance.

It is also advantageous that each sensor has a second resonator that canbe excited by a carrier frequency of the high-frequency energy. Thissecond resonator makes it possible to store the high-frequency energyfor a limited time, so that it is available for generating the answeringradio signal. This has the advantage, first, that the sensor forgenerating the answering radio signal need not rely on simultaneouslytransmitting the high-frequency energy through the antenna array,because during a pause in the supplying of high-frequency energy, thesecond resonator is capable of furnishing the energy required forsending the answering radio signal. Since there can be pauses in thesupplying of the high-frequency energy, it is conveniently possible touse the same antenna, at staggered times, both to supply thehigh-frequency energy to the sensors and to receive their answeringradio signal. Thus the first resonator makes it possible to constructthe sensor as a passive element, without its own power supply.

A further advantage of using the second resonator is that it enablesselective excitation of individual sensors by means of a polling radiosignal, with a carrier frequency tuned to the second resonator, or, inan environment in which at lead one sensor each is assigned to aplurality of polling units, it enables each polling unit and itsassigned sensors to be allocated a specific carrier frequency thatenables the polling units to answer and poll its assigned sensorsselectively.

As the second resonator, surface wave resonators are especiallypreferred.

Surface wave resonators of the kind that are capable of generating adelayed output oscillation pulse in reaction to an induced oscillationpulse are especially advantageous. During a first time interval that ismeant to be shorter than the delay in the second resonator, suchresonators can be excited to an oscillation; the energy stored in thisoscillation, however, is not available to the sensor as driving energyuntil there is a pause in the high-frequency energy supply through theantenna array. As long as the delay persists, the energy is stored inthe second resonator with only slight losses, dictated by theoscillation damping of the resonator substrate.

Such a delay can be achieved easily with the aid of a propagationdistance for the surface wave that a surface wave induced in the secondresonator must traverse before it is picked up.

Such resonators can be embodied for instance as surface wave filters,with a first pair of electrodes for inducing the surface wave and with asecond pair of electrodes, three-dimensionally spaced apart from thefirst, for picking up the surface wave; the two pairs of electrodes canbe separated from one another by the propagation distance.

Alternatively, they can be embodied as resonators with a single pair ofelectrodes, which then serves both to induce and to pick up the surfacewave; reflector electrodes are each spaced apart from the first pair ofelectrodes, for reflecting the surface wave, being propagated in theresonator substrate, with a time lag relative to the first pair ofelectrodes.

Further characteristics and advantages of the invention will becomeapparent from the ensuing description of exemplary embodiments inconjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Shown are

FIG. 1, a schematic illustration of a vehicle wheel that is equippedwith a sensor system of the invention, in a first exemplary embodiment;

FIG. 2, a schematic illustration of a vehicle wheel that is equippedwith a sensor system of the invention, in a second exemplary embodiment;

FIG. 3, a block diagram of a sensor of the vehicle wheel of FIG. 1;

FIG. 4, a block diagram of a polling unit for the sensor of FIG. 2;

FIG. 5, the course over time of the intensities of the radio signals atthe antenna array of the polling unit of FIG. 3;

FIG. 6, a first example for the makeup of a surface wave resonator thatis suitable as a second resonator for a sensor such as the sensor ofFIG. 2;

FIG. 7, a second example for the makeup of a surface wave resonator; and

FIG. 8, the course over time of the intensities of the radio signals atthe antenna array when a second resonator of the type shown in FIG. 5 orFIG. 6 is used.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a first example of a vehicle wheel, with a pneumatic tire30 that is equipped with a sensor system of the invention. Many sensors33 are disposed in the running surface of the pneumatic tire; they canfor instance be embedded in tread elements of the pneumatic tire, or inthe region of the (steel) jacket.

The sensors 33 may be capacitive or inductive sensors, whose makeup andmode of operation will be addressed in further detail hereinafter inconjunction with FIG. 3.

The sensors 33 are intended for measuring the deformation of the profileof the pneumatic tire 30 in a subregion of the pneumatic tire 30, namelyin its flattened contact face 32 with the road.

An antenna 11 is disposed in the vicinity of the axle of the wheel andhas a directional characteristic oriented toward the flattened region32; this directional characteristic is represented here by the lobe 34.

The antenna 11 is part of a polling unit, which is shown in FIG. 4 inthe form of a block diagram. An oscillator 13 is located in the pollingunit and generates a signal, here called the polling carrier signal,with a carrier frequency f_(T) in the range of 2.54 GHz. The carrierfrequency is preferably purposefully variable by several MHz. A secondoscillator 14 generates a polling measurement signal in the form of anoscillation with a frequency f_(M) in the range from 0 to 80 MHz. Whenthe polling unit is used to poll a plurality of sensors, the measurementfrequency f_(M) is expediently also variable purposefully, specificallyin increments that correspond to the size of the resonant range of afirst resonator of the sensors, which will be addressed in furtherdetail hereinafter.

A modulator 15 is connected to the two oscillators 13, 14 and modulatesthe polling measurement signal to the polling carrier signal and thusgenerates a polling radio signal that is output to a switch 12. Theswitch 12 is under the control of a timer 16, which alternately connectsa sending and receiving antenna 11 with the output of the modulator 15and the input of a demodulation and measuring circuit 17, which acts asa processing device for extracting the values of the dimensionalvariables to be detected from the answering radio signals received. Themodulation performed by the modulator 15 can in particular be amplitudemodulation or quadrature modulation; the demodulation performed in thedemodulation and measuring circuit 17 is complementary to it.

The makeup of the sensors 33 is shown in FIG. 3 in the form of a blockdiagram. The polling radio signal broadcast by the antenna 11 isreceived by an antenna 1 of the sensor shown in FIG. 3. A demodulationdiode 2, such as a Schottky or detector diode, is connected to theantenna. Such a diode is distinguished by an essentially paraboliccharacteristic curve even in the vicinity of the origin in thecoordinate system and thus by a highly nonlinear behavior, which leadsto mixing of the spectral components contained in the polling radiosignal, and thus to the generation of a spectral component with thefrequency f_(M) of the measurement signal at the output of thedemodulation diode 2. The spectral component at the carrier frequencyf_(T) that also appears at the output of the demodulation diode 2 servesto excite a resonator 3, in this case called the second resonator.

A low-pass filter 4, and downstream of the low-pass filter 4, aso-called first resonator 5 are connected to the output of thedemodulation diode 2; together with an element 6 sensitive to thedimensional variable, this first resonator forms an oscillating circuit.The first resonator 5, just like the second resonator 3, is acommercially available component, such as a quartz oscillator or asurface wave resonator. By means of the interconnection with thesensitive element 6, the resonant frequency of the first resonator 5 isvariable as a function of the dimensional variable.

The purpose of the low-pass filter 4 is essentially to keep spectralcomponents in the range of the carrier frequency f_(T) away from thefirst resonator 5 and thus to prevent their dissipation in the firstresonator 5. In this way, the low-pass filter 4 on the one handaccomplishes more-effective excitation of the second resonator 3, aslong as the polling radio signal is being received by the antenna 1;when there is a pause in the polling radio signal, the low-pass filter 4also limits the attenuation of the second resonator 3.

The sensitive element 6 is an inductive or capacitive element, such as amicromechanical pressure sensor element with two capacitor platesmovable relative to one another as a function of an exerted force oracceleration. Such an element 5 essentially affects only the resonantfrequency but not the attenuation of the first resonator 5.

Since such a sensor is sensitive only to a force or accelerationcomponent in one direction in space, three sensors 33 are provided atevery circumferential position 31 on the pneumatic tire 30 of FIG. 1:two sensors for the directions tangential to the surface of thepneumatic tire, one being in the direction of vehicle travel and theother being transverse to it, and a third sensor for the radialdirection.

FIG. 5 schematically illustrates the course of the reception fieldintensity P at the antenna 11 of the polling unit as a function of thetime t in the course of one polling cycle. The reception field intensityP is plotted on a logarithmic scale. During a period of time from t=0 tot=t₁, the polling radio signal is broadcast and is thus necessarily someorders of magnitude stronger than the echo signals thrown back from theenvironment of the polling unit or than an answering signal possiblyfurnished by a sensor.

At time t₁, the switch 12 connects the antenna 11 with the demodulationand measuring circuit 17 and the broadcasting of the polling radiosignal is interrupted. During a brief period of time [t₁, t₂], echos ofthe polling radio signal arrive at the antenna 11, having been thrownback by obstacles various distances away in the environment of theantenna 11.

Once these echo signals have faded, the only signal that then arrives atthe antenna 11 is an answering radio signal, which has been generated inthe sensor 33 by mixing of the oscillations of the two resonators 4, 5by the diode 2 functioning as a modulator and has been broadcast via theantenna 1. The demodulation and measuring circuit 17 therefore waits outa predetermined length of time Deltat after the switchover of the switch12 before beginning to examine the answering signal received at theantenna 11 as to its frequency and/or attenuation and thus to extractthe information it contains about the dimensional variable.

The delay Deltat can be fixedly specified as a function of thetransmission and reception power of the polling unit, for example insuch a way that for a given model of polling unit, a maximum range atwhich echo signals are still detectable by the polling unit isdetermined, and the delay Deltat is selected to be at least twice thetransit time that is equivalent to this range.

Since during the delay period Deltat the oscillations of the resonators3 and 5 also face, however, it is more advantageous to select as shortas possible a delay period Deltat as a function of the particularenvironment in which the polling unit is used; for example for aspecific usage environment, the maximum distance of a potential echosource from the polling unit is determined, and the delay is selected tobe at least equal to twice the signal transit time from the sensorelement to the polling unit, and thus precisely long enough that an echofrom that source will not be evaluated. In the sensor system shown inFIG. 1, the time equivalent to the transit time of a radio signal fromthe antenna 11 to the roadway in the vicinity of the flattened region 32and back to the antenna 11 again can be selected as the delay periodDeltat.

FIG. 6 shows that the second resonator has two spaced apart pairs 25, 26of electrodes 21, 22, with a spacing distance L. The electrodes 21, 22have a plurality of comb-like fingers 24 that engage in on another. Suchresonators, for example, can be formed as surface wave filters with afirst electrode pair 25 for stimulating the surface waves and a spacedapart electrode pair 26 for reading the surface wave, whereby the twoelectrode pairs 25, 26 are separated from one another by a spacingdistance L.

FIG. 7 shows that the second resonator has a pair 27 of electrodes 21,22 for stimulating and reading a surface wave and reflector electrodes23 arranged to be spaced apart from the electrode pair 27. Theelectrodes 21, 22 have a plurality of comb-like, parallel fingers 24that engage in one another. The reflection electrodes 23, respectively,have parallel fingers. The resonators can be formed with an individualelectrode pair 27, whereby the individual electrode pair 27 serves tostimulate as well as reade the surface wave. Reflector electrodes 23 arearranged, respectively, at a distance from the electrode pair 27. Inorder to reflect surface waves propagated in the substrate of theresonators with a time delay to the electrode pair 27.

FIG. 8 schematically illustrates the course of the reception fieldintensity P at the antenna 11 of the polling unit as a function of thetime t in the course of one polling cycle that results when a surfacewave resonator of the design shown in FIG. 6 or FIG. 7 is used as thesecond resonator of the sensor.

Just as in the case of FIG. 5, the polling radio signal is broadcastduring a time period from t=t₀ to t=t₁. At time t₁, the broadcasting ofthe polling radio signal is interrupted; the reception field intensity Pat the antenna 11 decreases to the extent that echos of the pollingradio signal that are thrown back from the environment of the antenna 11fade.

At time t₃=t₁+τ (ignoring signal transit times between the polling unitand the sensor), the surface wave, which has been induced in the secondresonator 3 by the sensor during the reception of the polling radiosignal, begins to reach the pair of electrodes at which it is picked up,so that from time t₃ on, a modulated answering radio signal is generatedat the sensor. Because the length of the second resonator 3 or the delayτ within this resonator 3 is selected to be great enough, it is possibleto achieve a pause in reception, between the fading of the echos at timet₂ and the arrival of the answering radio signal at time t₃, ofnegligible reception field intensity, which is detectable by thedemodulation and measuring circuit 17 of the polling unit and allows thepolling unit to distinguish unambiguously between an echo and ananswering radio signal. At time t₄=t₁+τ, the surface wave oscillationhas completely traversed the electrode pair that is picking up thesignal, and the generation of the answering radio signal ceases.

After a brief further delay, upon renewed broadcasting of the pollingradio signal at time t₅, a new work cycle of the polling unit of thesensor begins.

FIG. 2 shows a more sophisticated embodiment of the sensor system ofFIG. 1. Here only two sensors 33 are disposed at each position 31 on thecircumferential surface of the tire, and each sensor is sensitive toeither force or acceleration in the directions tangential to the surfaceof the pneumatic tire. Their makeup is the same as described above inconjunction with FIG. 1, 3, 5 or 6.

The sensor, sensitive to a force or acceleration in the radialdirection, located at each position 31 in FIG. 1 is replaced here by asingle sensor 36, which measures the dynamic internal pressure of thepneumatic tire. From this internal pressure, or its changes, aconclusion can be drawn as to the force acting on the pneumatic tire 30in the radial direction. This sensor 36 has an antenna 37 or antennaarray, which extends to some length along the circumferential directionof the pneumatic tire and one part of which, in every rotationalposition of the pneumatic tire, is located inside the lobe 34 of theantenna 11, so that the pressure sensor 36 can be polled at anyarbitrary instant.

The single pressure sensor 36 thus replaces all the sensors for theforce or acceleration in the radial direction of the exemplaryembodiment of FIG. 1. This makes a considerable reduction in the numberof sensors possible, compared to the exemplary embodiment of FIG. 1. Forinstance, assuming a circumference of the pneumatic tire 30 of about 2meters and a spacing between positions 31 of the individual sensors ofabout 10 cm, the number of sensors required is reduced from 3×20=60 inthe case of the exemplary embodiment of FIG. 1 to 2×20+1=41 in the caseof FIG. 2.

In the exemplary embodiments shown in FIGS. 1 and 2, the length of thelobe 34 in the circumferential direction and the spacing of the sensorpositions is selected such that at every instant, three positions 31 arelocated inside the lobe 34. This means that at every instant, eithernine or seven sensors (six sensors 33 for the tangential directions, andthe pressure sensor 36) can be addressed by the polling radio signal ofthe antenna 11. For usable remote polling, it is necessary to be able todistinguish between the answering radio signals that originate at aplurality of sensors disposed at the same position and the answeringradio signals furnished by sensors at different positions 31. To thatend, coding of the radio signals is necessary. Software coding is notappropriate here, first because of the processing times associated withexecuting a program and second because the sensors can obtain the energyrequired for such coding only from the polling radio signal, and suchenergy is scarce.

Coding with the aid of the carrier and measurement frequencies of theradio signals exchanged between the antenna 11 and the sensors istherefore employed. The sensors 33 distributed over the circumference ofthe pneumatic tire 30 are each divided up into a plurality of groups; inthe examples of FIGS. 1 and 2 this number of groups has been arbitrarilydefined as four, and depending on which of the four groups their sensors33 belong to, the positions 31 are each marked a, b, c, or d in FIGS. 1and 2.

In a first variant, the carrier frequency f_(T) of the polling radiosignal is the same for all of the sensors 33, and the second resonators3 of all the sensors 33 are tuned to this carrier frequency f_(T). Thefirst resonators have tuning ranges that differ within a group dependingon the dimensional variable to be detected by the sensor 33 and thatmoreover differ from one group to another. In the case of FIG. 2, forexample, if it is assumed that the tuning ranges of the first resonators5 each have a width of 1 MHz, then the following association of tuningranges with groups and dimensional variables can be made:

Group Force in travel direction Force in traverse direction a  0-10 MHZ40-50 MHZ b 10-20 MHZ 50-60 MHZ c 20-30 MHZ 60-70 MHZ d 30-40 MHZ 70-80MHZ

The polling unit is thus capable, by selecting the measurementfrequency, of selectively exciting only the first resonators of ongroup, and within this group only the first resonators of the sensor 33that is associated with a certain dimensional variable, so that theanswering radio signal received following this excitation can only comefrom the sensor 33 thus addressed.

It is understood that it is also possible to modulate a plurality ofmeasurement frequencies to the answering signal, so that answering radiosignals are received simultaneously from a plurality of sensors 33, andthe measurement frequencies of the answering radio signals that overlapchronologically can be broken down spectrally in the polling unit, so asto associate them with the individual sensors 33, or the dimensionalvariables monitored by them.

Another possibility is to assign different carrier frequencies, in thesame tuning ranges of the first resonators 5, to various sensors 33disposed at the same position 31 and belonging to the same group. Inthis way, from each of these sensors answering radio signals can bereceived which while they have the same measurement frequencies, or moreprecisely measurement frequencies within the same tuning range, arenevertheless distinguishable from one another in the polling unit on thebasis of their different carrier frequencies and can thus be associatedcorrectly with the dimensional variables to be detected.

If two dimensional variables are to be detected at one position 31, itmay also be expedient to construct the antennas 1 of the sensors 33 withpolarization sensitivity. For instance, the antenna 1 of a sensor 33that detects a force in the travel direction can be sensitive only to apolling radio signal polarized parallel to the travel direction, and asensor 33 disposed at the same position 31 for detecting the forcetransversely to the travel direction is sensitive to a polling radiosignal polarized transversely to the travel direction. The polarizationsof the answering radio signals broadcast by the two sensors 33 differcorrespondingly, so that the polling unit can distinguish the answeringradio signals from their polarization.

While the vehicle is in motion, all the sensors of the wheel should bepolled continuously. To that end, in a simple embodiment, the lobe 34 ofthe antenna 11 can be dimensioned such that essentially only oneposition 31 at a time is ever located inside the lobe 34. To avoidinterference with the dimensional variable from sensors located at theperiphery of the lobe 34, a very sharply defined spatial boundary of thelobe 34 is necessary in that case.

In an advantageous alternative in this respect, the size of the lobe 34of the antenna 11 in the circumferential direction of the pneumatic tire30 is on the one hand large enough that a plurality of positions 31 arealways located inside this lobe 34, yet on the other hand not so largeenough for there to be room in it for the sensors of all the groups. Inthe position of the wheel shown in FIG. 1 and FIG. 2, the polling unitcan excite sensors in each of the groups c, d and a and receiveanswering radio signals from them, but sensors of group b are notlocated in the lobe 34. Since the groups a, b, c, d follow one anothercyclically, the polling unit can conclude from the absence of ananswering radio signal from group b that the sensors of groups a and cmust be located in the vicinity of the edge of the flattened region 32,and that the sensor of group d must be located in the middle of theflattened region 32. At the edge of the region 32, there is a strongflexing motion on the part of the material comprising the pneumatic tire30, and as a result the sensors of groups a and c can be subjected topowerful forces. The sensor of group d, conversely, must be located inthe middle of the flattened region 32, i.e. at the place where theflexing motion is only slight, yet the transmission of force between thepneumatic tire 30 and the roadway is most effective. The answering radiosignal furnished by this sensor thus makes it possible to draw theprecisest possible conclusion about the quality of road adhesion of thepneumatic tire. The polling unit therefore identifies the answeringradio signal of the sensor of group d from its characteristicmeasurement frequency and for instance causes a warning signal to beoutput to the vehicle driver if the instantaneous value of thismeasurement frequency, which represents the force detected by the sensorin group d, departs from a desired range. In this way the driver can bewarned even before the road adhesion of the vehicle is lost, forinstance from aquaplaning or traveling on an icy surface, and the riskof accidents can be reduced.

1. A sensor system for detecting at least one dimensional variable of arotating object (30), having at least one sensor, disposed on therotating object (30) and sensitive to the dimensional variable, andhaving means for picking up measurement signals from the at least onesensor and forwarding the signals to a processing device, which includean antenna array (11) for supplying the at least one sensor withhigh-frequency energy end for receiving a high-frequency signal,modulated as a function of the variable to be detected, from the sensor,characterized in that a plurality of such sensors are disposed on theobject (30), distributed in the circumferential direction; and that theantenna array (11) has a directional characteristic (34) fortransmission and/or reception which is stationary with respect to acoordinate system not rotating with the object (30) and which includesonly a subregion (32) of the object (30).
 2. The sensor system of claim1, wherein the subregion is the contact face of the object (30), with asubstrate.
 3. The sensor system of claim 1, wherein the antenna array(11) includes a common antenna for transmission and reception.
 4. Thesensor system of claim 1, wherein sensors used to detect the samephysical variable have a spacing in the circumferential direction of theobject (30) that is essentially equivalent to the length of thesubregion (32) in the circumferential direction.
 5. The sensor system ofclaim 1, wherein the sensors have coding, which makes it possible tosupply high-frequency energy selectively to at least one sensor fromamong a plurality of sensors located in the subregion (32), or toreceive selectively from at least one sensor located in the subregion.6. The sensor system of claim 5, wherein the sensors form a predefinednumber of groups, which are each distributed cyclically over thecircumference of the object (30).
 7. The sensor system of claim 6,wherein the subregion is defined such that the sensors of all of thepredefined number of groups are never all located in it at the sametime.
 8. The sensor system of claim 1, wherein each sensor has a firstresonator (5), which can be excited by a modulated measurement frequencyof a carrier frequency of the high-frequency energy, and whose resonantfrequency is variable as a function of the dimensional variable.
 9. Thesensor system of claim 8, wherein the first resonator (5) includes asurface wave resonator or a quartz oscillator.
 10. The sensor system ofclaim 9, wherein the first resonator (5) further includes a discretecomponent (6) that is sensitive to the dimensional variable.
 11. Thesensor system of claims 5, wherein one specific resonator tuning rangecorresponds to each coding.
 12. The sensor system of claim 11, whereinthe resonator tuning ranges of the individual codings are disjoint. 13.The sensor system of claim 1, wherein the dimensional variable is avectorial variable, and in particular a force or acceleration.
 14. Thesensor system of claim 13, wherein the sensors are each designed fordetecting two components of the dimensional variable that areperpendicular to one another and tangential to the surface of theobject.
 15. The sensor system of claim 1, wherein the object (30) is apneumatic tire.
 16. The sensor system of claim 15, wherein it also hasan individual sensor (36) for the tire pressure.
 17. The sensor systemof claim 1, wherein each sensor has a second resonator (3) that can beexcited by a carrier frequency of the high-frequency energy.
 18. Thesensor system of claim 17, wherein the second resonator (3) is a surfacewave resonator.
 19. The sensor system of claim 18, wherein the secondresonator (3) is capable of generating a delayed output oscillationpulse in reaction to an induced oscillation pulse.
 20. The sensor systemof claim 19, wherein the second resonator (3) has a propagation distance(L) for the surface wave that a surface wave induced in the secondresonator (3) must traverse before it is picked up.
 21. The sensorsystem of claim 19, wherein the second resonator has twothree-dimensionally spaced-apart pairs (25, 236) of electrodes (21, 22).22. The sensor system of claim 19, wherein the second resonator has onepair (27) of electrodes (21, 22), for inducing and picking up a surfacewave, and reflector electrodes (23), spaced apart from the pair (27) ofelectrodes.